The corrosion of metal surfaces which are in contact with aqueous systems is a common problem. Corrosion may occur in various locations including boiler feedwater lines, heaters, steam lines, process tanks and return lines. Dissolved oxygen in the aqueous system is often a principal factor influencing the formation of the corrosion, particularly where iron and steel are the materials of construction. The corrosion of iron based metals in conventional boiler systems is a well known problem, and controlling the presence of oxygen in boiler systems, particularly in the feedwater section has received considerable attention. Oxygen removal may be partially accomplished by either vacuum or thermal deaeration, or both. Complete removal of oxygen cannot be effected by these means, however, and further removal by use of a chemical oxygen scavenging agent, such as sodium sulfite, has been a customary practice.
Recently, the use of low pressure boilers (i.e. those operating below about 150 psig) has been increasingly supplanted by the use of boilers operating at moderate pressure (i.e. operating between about 150 psig and about 600 psig) and high pressure (i.e. operating above about 600 psig). As boiler operating temperatures and pressures have increased, there has been particular interest in the performance of chemical oxygen scavengers which are effective at these operating conditions. The use of sulfites at elevated temperatures and pressures has been known to result in the formation of sulfur dioxide and hydrogen sulfide, which can be a source of corrosion. Other scavenging agents such as hydrazine, hydroquinone, and certain hydroxylamines have been found to perform satisfactorily in some circumstances. For example, U.S. Pat. No. 4,278,635 to Kerst discloses the use of various dihydroxy, diamino, and amino hydroxy benzenes and their lower alkyl substituted derivatives, and particularly hydroquinone, as corrosion control agents in boiler systems. U.S. Pat. No. 4,282,111 to Cuiba also relates to the use of hydroquinone to reduce the oxygen content of an aqueous medium. U.S. Pat. No. 4,363,734 to Solvinsky discloses the use of hydroquinone as a catalyst in combination with dihydroxy acetone. Japanese Patent Publication No. SHO 51-93741 by Suzuki et al reports synergistic inhibition of metallic corrosion by combinations of dihydroxybenzenes (e.g. hydroquinone and methyl hydroquinone) and various carboxylic acids in boiler water systems. In other circumstances, the efficiency with which the scavenging proceeds has not been optimal. There is thus a continuing need for alternative oxygen scavengers which can be effectively used at elevated temperatures and pressures.
U.S. Pat. No. 2,170,596 to Ouiggle describes oxygen absorbing solutions using catalysts such as various quinones together with reducing agents such as reducing sugars like glucose. U.S. Pat. No. 1,988,823 to Winning et al describe rust remover compositions which comprise ammonium salt, an alkali salt of a water soluble organic acid, sugar, and an inhibitor of corrosion such as pyrogallol, hydroquinone, pyridine or quinoline.
Gluconic acid and its salts have been used for corrosion control. U.S. Pat. No. 2,529,178 to Nieland et al discloses the use of gluconates such as sodium gluconate to protect metals, particularly ferrous metals, from corrosion in water systems. This patent describes the formation of a protective layer on the metal surface when certain amounts of the gluconate are added to the water in the system.
U.S. Pat. No. 3,589,859 to Foroulis discloses that gluconate salts, particularly when used in combination with a benzoate or a salicylate salt, inhibits the oxidative corrosion in aerated cooling systems. U.S. Pat. No. 3,711,246 to Foroulis is directed to inhibiting oxidative corrosion in an oxygen-containing cooling water system using certain inorganic silicate salts together with certain gluconate salts, optionally with certain polyphosphates.